There's more to it than that. Petzval has become a catch-all term for
"swirly bokeh" but back in the day, these were not used to generate swirl.
The swirl only comes from shooting them on a larger format than intended,
generally. Some of the older lenses had various methods of adding
soft-focus, which is now a "craze" in the large-format world. Any brass
lens gets overpriced generally, as people succumb to the craziness.
Generally it's not vignetting that adds the swirl, it's more spherical
aberrations and other factors. It's a fairly complex topic and when you
add in deliberate soft-focus methods becomes even more complex.
Generally the smoothest bokeh will be one stop down from wide-open.
Wide-open tends to be busy with overly accentuated hard-edges on
highlights.
-Ed
On 8/22/14 6:16 AM, "olympus-request@xxxxxxxxxxxxxxxxx"
<olympus-request@xxxxxxxxxxxxxxxxx> wrote:
>I think it was the style with Petzval lenses lenses in LF and the
>recent expensive incarnations available ---just like buttery smooth may
>be the style to some degree now in some quarters. I think it is not due
>to any optical characteristics per se, but just internal vignetting.
>One can mimic this with just about any lens by masking the front
>element to an aperture just larger than the entrance pupil (at the
>price of substantial vignetting).
--
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